The present invention relates to a multi-beam scanning apparatus for use in image forming apparatuses such as laser printers and laser copying machines.
Generally, a beam scanning apparatus scans a surface to be scanned of a photoconductor or other photoconductive member by deflecting a diverging light, which is emitted by a light source unit and which passes through a collimating lens, a cylindrical lens and other lens elements, with a deflector, such as a rotating polygonal mirror, and by imaging the deflected light via an imaging lens. The light source unit includes a semiconductor laser chip to emit light from both sides (front and back) of the laser chip, a photodiode to monitor the light emitted from the back of the semiconductor laser chip, and a case housing the semiconductor laser chip and the photodiode. The case has an opening for allowing the light emitted from the front side of the laser chip to emerge from the case. The light emitted by the semiconductor laser chip is modulated by a modulator according to an image signal, and an image is written on the surface to be scanned of the photoconductor with the modulated light to form a latent image.
Japanese patent laid-open publication No. 5-27189 describes a beam scanning apparatus, in which light, which is emitted from the back of a semiconductor laser chip, dispersed by an internal surface of a laser substrate defining a case of the laser chip, and emerged from an opening of the case as a dispersing light, is intercepted by an intercepting member arranged between a collimating lens and a light source unit so as not to reach the collimating lens. JP No. 527189 further describes another beam scanning apparatus in which the intercepting member functions also as a diaphragm.
In the beam scanning apparatus of JP No. 5-27189, however, because the intercepting member is arranged in the vicinity of a light emitting point of the light source unit, the intercepting member may intercept the light which is emerged from the front surface of the semiconductor laser chip and is desired to reach the collimating lens for scanning. In order to arrange the intercepting member so as not to intercept such light required for scanning, on the other hand, the light emitted from the back of the semiconductor laser chip, dispersed by the internal surface of the laser case and emerged from the opening of the laser case may not be sufficiently and effectively intercepted by the intercepting member.
Further, when using the intercepting member as the diaphragm in the apparatus of JP 5-27189, the intercepting member must be arranged in the vicinity of the light emitting point and must be located at a position along the light path where the light flux is diverging. Thus, a relatively high positional accuracy is required for the intercepting member.
Furthermore, the scanning apparatus of JP No. 5-27189 requires a relatively large allowance for adjusting the light quantity because the variation of the light quantity is relatively large between the light source units.
When the light source unit includes a plurality of light emitting points, the photodiode for monitoring the light becomes larger than when the light source unit has a single light emitting point by a factor that substantially corresponds to the number of light emitting points. Therefore, the light source unit having a plurality of light emitting points tends to more easily generate dispersed light other than the scanning light. For example, when the photodiode for the light source unit having a single emitting point is 20 square xcexcm, the photodiode for the light source unit having four light emitting points becomes about 80 square xcexcm, i.e., four times larger. Further, the opening for emerging light also needs to be enlarged, which increases the possibility that dispersed light other than the light needed for scanning (sometimes referred to as ghost light) emerges from the case.
In order to overcome the problems described above and other problems, preferred embodiments of the present invention provide a novel multi-beam scanning apparatus that prevents dispersed light, which is generated by the reflection of a light flux from a semiconductor laser chip via a surface of a light receiving element provided for monitoring the light flux, from reaching a surface to be scanned and from forming an abnormal image on the surface to be scanned.
Preferred embodiments of the present invention further provide a novel multi-beam scanning apparatus that eliminates only unnecessary dispersed light without intercepting light that is necessary to form an image on a surface to be scanned.
Further, preferred embodiments of the present invention provide a novel multi-beam scanning apparatus that prevents the reflection of light by an intercepting member, which is intercepting unnecessary dispersed light, to prevent the intercepting member from generating additional dispersed (ghost) light.
Furthermore, preferred embodiments of the present invention provide a novel multi-beam scanning apparatus that prevents dispersed light, generated by the reflection of light from a surface of an intercepting member provided for intercepting unnecessary dispersed light, from reaching a surface to be scanned and thereby causing formation of an abnormal image on the surface to be scanned.
Still furthermore, preferred embodiments of the present invention provide a novel multi-beam scanning apparatus that effectively and efficiently eliminates dispersed light generated by the reflection of light via a surface of a light receiving element which monitors light in a light source unit.
Another preferred embodiment of the present invention provides a novel multi-beam scanning apparatus that suppresses the reflection of light by a surface of a cover of a deflector to prevent additional ghost light from being generated by the cover.
Another preferred embodiment of the present invention further provides a novel multi-beam scanning apparatus that prevents dispersed light, generated by the reflection of light via a surface of a cover of a deflector, from reaching a surface to be scanned and causing formation of an abnormal image on the surface to be scanned.
According to another preferred embodiment of the present invention, a multi-beam scanning apparatus includes a light source having a semiconductor laser chip in which a plurality of light emitting points are arranged such that optical beam spots are arranged at a predetermined interval in a sub-scanning direction on a surface to be scanned. A light receiving element receives a light flux from the semiconductor laser chip for monitoring the light. A case houses therein the semiconductor laser chip and the monitoring light receiving element, and has an opening for emerging the light emitted from a surface of the semiconductor laser chip. A coupling lens couples a divergent light flux from the light source with a subsequent system. A deflector deflects the light flux. A first imaging system arranged between the coupling lens and the deflector has a power in the sub-scanning direction so as to transform the light flux from the coupling lens into a substantially linear image in a vicinity of a deflecting surface of the deflector. A second imaging system images the deflected light flux into an optical beam spot on the surface to be scanned. An intercepting member is arranged between the light source and the surface to be scanned to intercept light, which is emitted from the back of the semiconductor laser chip and dispersed in the case and passes the opening, before reaching the surface to be scanned.
According to a preferred embodiment of the present invention, the intercepting member may be arranged so as not to intercept scanning light which is provided and used for forming an image on the surface to be scanned. Further, the intercepting member may have either a reflection preventing coating or a reflection preventing treatment, or may be made of a material having a low reflectance.
Furthermore, the intercepting member may be angled such that the dispersed light does not reach the surface to be scanned in a main scanning direction. Also, the intercepting member may have either an angle of elevation or an angle of depression relative to a scanning plane so that the dispersed light does not reach the surface to be scanned. The intercepting member may also preferably be arranged between the coupling lens and the deflector.
According to another preferred embodiment of the present invention, a multi-beam scanning apparatus transforms a divergent light flux from a light source having a plurality of light emitting points into a linear image in a vicinity of a deflecting surface of a deflector, and images the light flux deflected by the deflector on a surface to be scanned as an optical beam spot. The light source includes a semiconductor laser in which a semiconductor laser chip is accommodated in a laser chip case having an opening for emerging light. A light emitted from a back of the semiconductor laser chip is dispersed in the laser chip case, and an emerging direction of the dispersed light is set such that the dispersed light passed though the opening reaches portions and locations on the surface to be scanned other than an image writing area.
According to preferred embodiments of the present invention, the emerging direction of the dispersed light may be directed toward a cover of the deflector. Further, the cover may be provided with reflection preventing coating or reflection preventing treatment, or a low reflectance member may be provided as part of the cover including parts where the dispersed light is impinged upon.
Further, the cover may be configured such that a direction of the dispersed light reflected by the cover leads to an outside of the image forming area in a man scanning direction.
Furthermore, a reflecting surface of the cover may be angled such that the dispersed light reflected by the cover leads to an outside of the image forming area in a sub-scanning direction.